Procedures for preparing photographic images in silver by diffusion transfer principles are well known in the art. For the formation of the positive silver images, a latent image contained in an exposed photosensitive silver halide emulsion is developed and almost concurrently therewith, a soluble silver complex is obtained by reaction of a silver halide solvent with the unexposed and undeveloped silver halide of said emulsion. The photosensitive silver halide emulsion is developed with a processing composition in a viscous condition which may be spread between the photosensitive element comprising the silver halide emulsion and a second element which may comprise a suitable silver precipitating layer. The processing composition effects development of the latent image in the emulsion and, substantially contemporaneously therewith, forms a soluble silver complex, for example, a thiosulfate or thiocyanate, with undeveloped silver halide. This soluble silver complex is, at least in part, transported in the direction of the print-receiving layer and the silver thereof is largely precipitated in the silver-precipitating element to form a positive image thereon. Procedures of this description are disclosed, for example, in U.S. Pat. No. 2,543,181 issued to Edwin H. Land. See, also, Edwin H. Land, One Step Photography, Photographic Journal, Section A, pp. 7-15, January 1950.
Additive color reproduction may be produced by exposing a photosensitive silver halide emulsion through an additive color screen having filter media or screen elements each of an individual additive color, such as red or green or blue, and by viewing the reversed or positive silver image formed by transfer to a transparent print-receiving element through the same or a similar screen which is suitably registered with the reversed positive image carried by the print-receiving layer.
As examples of suitable film structures for employment in additive color photography, mention may be made of U.S. Pat. Nos. 2,861,885; 2,726,154; 2,944,894; 3,536,488; 3,615,427; 3,615,428; 3,615,429; 3,615,426; and 3,894,871.
The image-receiving elements of the present invention are particularly suited for use in diffusion transfer film units wherein there is contained a positive transfer image and a negative silver image, the two images being in separate layers on a common, transparent support and viewed as a single, positive image. Such positive images may be referred to for convenience as "integral positive-negative images", and more particularly as "integral positive-negative transparencies." Examples of film units which provide such integral positive-negative transparencies are set forth, for example, in the above-indicated U.S. Pat. Nos. 3,536,488; 3,894,871; 3,615,426; 3,615,427; 3,615,428; and 3,615,429.
In general, silver-precipitating nuclei comprise a specific class of adjuncts well known in the art as adapted to effect catalytic reduction of solubilized silver halide specifically including heavy metals and heavy metal compounds such as the metals of groups IB, IIB, IVA, VIA and VIII and the reaction products of Groups IB, IIB, IVA and VIII metals with elements of Group VIA.
Particularly preferred precipitating agents are noble metals such as silver, gold, platinum, palladium, etc., and are generally provided in a matrix as colloidal particles.
U.S. Pat. No. 3,647,440, issued Mar. 7, 1972 discloses receiving layers comprising finely divided nonsilver noble metal nuclei obtained by reducing a noble metal salt in the presence of a colloid or binder material with a reducing agent having a standard potential more negative than -0.30. It is the thrust of the patent that a reducing agent having a standard potential more negative than -0.30 must be used in order to obtain nuclei of a specific, usable size range. It is further illustrated that stannous chloride, which does not fall within the standard potential range, does not produce useful nuclei. The binder materials disclosed include gelatin, polyvinyl pyrrolidone, polymeric latices such as copoly (2-chloroethyl-methacrylate-acrylic acid), a mixture of polyvinyl alcohol and the interpolymer of n-butyl acrylate, 3-acryloyloxy-propane-1-sulfonic acid, sodium salt, and 2-acetoacetoxyethyl methacrylate, polyethylene latex, and colloidal silica. The amount of colloid binder employed ranges from about 5 to 500 mgs/ft.sup.2 with the nuclei ranging from 1 to 200 micrograms/ft.sup.2.
Copending application Ser. No. 69,282, filed Aug. 24, 1979 (common assignee) discloses and claims a receiving element for use in an additive color photographic diffusion transfer film unit which comprises a transparent support carrying an additive color screen and a layer comprising noble metal silver-precipitating nuclei and a polymer; wherein the nuclei are present in a level of about 0.1-0.3 mgs/ft.sup.2, and said polymer is present at a level of from about 0.5 to 5 times the coverage of said nuclei. Preferably, the noble metal is obtained by reduction of a noble metal salt or complex, and more preferably, the noble metal is palladium. The preferred binder polymers are gelatin and hydroxyethyl cellulose; gelatin at the low end of the nuclei-binder ratio can be employed to provide good density and neutral tone positive images in the receiving layer whereas the preferred levels of other polymers, such as hydroxyethyl cellulose, are at the higher portions of the nuclei-binder range.
Copending application Ser. No. 897,942, filed Apr. 4, 1978, (common assignee) now U.S. Pat. No. 4,168,015 issued Jan. 29, 1980 discloses and claims a receiving element for use in a silver diffusion transfer film unit which comprises a support carrying a layer of noble metal silver-precipitating nuclei in a polymeric binder composition of polyvinyl alcohol and gelatin.
Copending application Ser. No. 897,943, filed Apr. 4, 1978, (common assignee) now U.S. Pat. No. 4,186,013 issued Jan. 29, 1980 discloses and claims a receiving element for use in a silver diffusion transfer film unit which comprises a support carrying a layer of noble metal silver-precipitating nuclei in a binder composition of hydroxyethyl cellulose and gelatin.
Copending application Ser. No. 897,945, filed Apr. 7, 1978, (common assignee) now U.S. Pat. No. 4,204,869 issued May 27, 1980 discloses and claims a method for forming noble metal silver precipitating nuclei which comprises the reduction of a noble metal salt or complex by a stannous salt wherein the stannous salt is partially oxidized prior to said reduction. Air, oxygen and hydrogen peroxide are disclosed as oxidizing agents.
The above-mentioned patents and applications are incorporated herein by reference in their entirety.